Saudi Arabia has promised to investigation the Yemen funeral airstrike

The Saudi Arabia-led alliance fighting rebel forces in Yemen has promised to investigate the deaths of 140 people in an airstrike after United States threatened to withdraw military support over the incident.

Saudi Arabia initially denied responsibility for Saturday’s bombing, which left 534 people wounded and turned a funeral gathering into what witnesses called “lake of blood.”

However, the alliance said in a statement on Sunday that it would invite US experts to participated in an “immediate investigation.”

“The coalition is also willing to provide the investigation team with any data and information related to its military operations today, at the incident’s location and the surrounding areas,” it said.

The announcement followed international outrage at one of the bloodiest incidents of the 18 month war in Yemen.

A spokesman for U.N. Secretary-General Ban Ki-moon said any deliberate attack against civilians was utterly unacceptable. Mr Ban called for “a prompt and impartial investigation of this incident. Those responsible for the attack must be brought to justice”, the spokesman said.

The White House warned that it would not provide a “blank check” to the Saudi-led alliance, which is fighting Iranian-backed Houthi rebels for control of the country, after the bombing of a funeral hall in Sanaa, the Yemeni capital.

“Even as we assist Saudi Arabia regarding the defence of their territorial integrity, we have and will continue to express our serious concerns about the conflict in Yemen and how it has been waged,” Ned Price, a National Security Council spokesman, said on Saturday. He also called for an immediate ceasefire.

Tobias Ellwood, Britain’s minister for the Middle East, said he had “raised concerns” with the Saudi ambassador to London and urged Riyad to pursue the investigation as “a matter of urgency.”

Rebel leaders accused the alliance of deliberately targeting the funeral, where they said hundreds of people had gathered to pay respects to the father of the interior minister of Houthi-run northern Yemen.

Ali Abdullah Saleh, a former president of Yemen who is allied to the rebels, called for attacks on the Saudi border to avenge the bombing. “I call upon all members of the armed forces, security and popular committees (militia)… to head to the front, to the borders, to take revenge,” he said in a televised address.

Mr Saleh, who stepped down in 2012, commands rebel soldiers who have allied with Iranian-backed Houthis, who seized the Yemeni capital in 2014.

The rebels are opposed by Abd-Rabbu Mansour Hadi, the internationally-recognized president, who is backed by the Saudi led alliance that also includes Bahrain, Egypt, Morocco, Qatar, Sudan and the United Arab Emirates.

An estimated 10,000 people have been killed in Yemen since the war began.

The United Nations blames coalition strikes for 60 percent of an estimated 3,800 civilian deaths since they began in March 2015.

Previous incidents include the September 2015 bombing of a wedding near the Red Sea city of Mokha, which killed at least 131 civilians.

In March this year, Saudi-led air raids on a market killed at least 119 people, including 106 civilians, in the northern rebel-held province of Hajja.

The mounting civilian death toll has led to criticism of the United States and Britain over their military support and arms sales to Saudi Arabia.

Fragments of shrapnel found by an ITV news crew at the site of Saturday’s bombing appeared to be from a US-made Mark 82 bomb.

Earlier this summer the United States scaled back the number of intelligence advisors assisting the mission in August, citing concerns over civilian casualties.